These are corn starch grains viewed with crossed circular polarized light.
The cross structure evident in starch grains with linear polarized light is absent because with
circular polarized light maximum retardation is shown regardless of the structures orientation in
the plane of the stage.

Transmitted Circular Crossed Polarized Light

Definition/Function:

Corn starch is derived from Zea mays. it is by far the most common starch grain encountered in the indoor environment.
It is used in paper sizing, coating plastics, coating candy, as a body powder, as a carrier for fragrances and pesticides,
as an extender in coatings and paints, a mold-release in formed polymer manufacture, and many other uses.

Starch grains are are a means for plants to store energy. They are produced by a wide variety of plants and are a mixture
of alpha-amylose and amylopectin. Starch grain differ in their size, their shape, and the structure of the center vacuole.
Many of these differences are useful for the identification of the plant of origin for the starch grain.

Significance in the Environment:

Starch is common in the indoor environment. It is widely used as a body powder, a carrier for fragrances, for
insecticides, for mold-release, and many other applications. Surgical gloves must be free of rice starch because rice
starch inside the body cavity can cause infection. Corn starch in the same body cavity has no effect.

Characteristic Features:

Corn starch tends to be polyhedral to subspherical in shape and generally 10 to 20 micrometers in diameter. The center
vacuole may be spherical but is generally an elongated scar with pointed ends. It may have from 2 to 5 points forming a
slit or star-like structure.

Associated Particles:

If corn starch is found with significant amounts of dog dander it may indicate the presence of an insecticide. People in
the locality should be questioned about the use of flea powders or powdered fresheners. When used as a body powder it is
often associated with other cosmetic particles. When it is a food residue then other food particles are generally present
and some cooked starch may be associated with the particles. When it is from a manufacturing process there are generally
other residues from that process present. When it is from paper sizing there are generally ink or toner particles and
significant amounts of paper fiber present.